On 10/29/21 10:26, J. Bruce Fields wrote:
On Fri, Oct 29, 2021 at 09:45:34AM -0400, bfields wrote:
On Thu, Oct 28, 2021 at 10:48:50AM -0400, Steve Dickson wrote:
This kernel patch and an upcoming nfs-utils patch
adds a new export option 's2sc' which will allow
inter server to server copies.
They're already allowed by a module option. Why is an export option
better? And why should it be set on the destination server and not the
source server?
Really, first I think we should try to identify what the problem is that
we're trying to solve.
I guess we're thinking: we expect server-to-server copy to be a win in
some cases, but not others.
Right!
What would those cases look like?
Say you've got a client "C" and two servers, "S" and "T", and C is
copying a file from S to T.
I'd expect bandwidth of the traditional read-write-loop copy to be the
minimum of the network bandwidth between S and C, and the network
bandwidth between C and T. Are there common cases were the S-to-T
bandwidth would be significantly less than both of those?
I was thinking the connection between S-to-T would be much
faster (come type of cluster interconnect) that the connection
between C-S or C-T.
My guess would've been that that's relatively unusual. So as a first
pass, just turning on COPY unconditionally doesn't seem so bad.
I know you're thinking about in cases where S and T are connected by a
high-performance network not necessarily available to C.
Exactly... well said.
In that case, we know we want to use server-to-server copy for copies
between S and T. But is it necessarily a problem to also use it for
copies between some other server and T? Also, does knowing the export
containing the destination file on T really tell you whether or not the
copy will be coming from S and not from some other server?
No... All the export is doing is allowing the COPY request
to succeed. I don't think T has any idea where the
COPY is coming from... but you would know better that I :-)
I'd think the bigger issue in that case is figuring out how to configure
S so that it returns the right IP address in the cnr_source_server field
of the COPY_NOTIFY reply. Currently we return address that the client
sent the COPY_NOTIFY, and I don't know if that's correct for that case.
I didn't look at this part of the transaction since it was
not controlled by the module param... But How would S know its the
"right IP address" since it is C that did the mount to T and
is giving S the address?
Keeping in context of what I'm trying to do... All I'm
trying to do is enable the feature, and with your points,
I think you are making my case there should be an
alternate of enabling these copies.
steved.
